1. Field of the Invention
The present invention relates to a power management method, more particularly to a power management method for a wireless communication apparatus.
2. Description of the Related Art
Referring to FIG. 1, an existing wireless communication apparatus 9, such as a wireless network card, is coupled to a host 90 and a communication device 99 (for example, a base station, an access point device, a peer-to-peer device, etc.) through a host transmission interface 91 and a wireless communication interface 92, respectively.
Power consumption of the wireless communication interface 92 is a major portion of overall power consumption of the wireless communication apparatus 9. Thus, the wireless communication interface 92 is generally designed to be target of power saving. For example, in the IEEE 802.11 standard, two types of power modes are provided; one is active mode (also called continuous aware mode) and the other one is power saving mode. A designer of the wireless communication apparatus 9 can design a communication protocol between the wireless communication interface 92 and the communication device 99 under the IEEE 802.11 standard such that the power consumption of the wireless communication apparatus 9 can be reduced when a traffic volume is relatively low. For example, in a current power management method, the wireless communication interface 92 enters the power saving mode when the wireless communication apparatus 9 does not receive packets within a predetermined length of time. However, when the packets are received, the wireless communication interface 92 is restored to the power saving mode only after the predetermined length of time has elapsed. In addition, in the power saving mode, the wireless communication interface 92 is woken at predetermined intervals for receiving signals from the communication device 99 so as to maintain connection with the communication device 99. It can be seen that, in the existing power management method for the wireless communication interface 92, there is still much time periods in which the power consumption of the wireless communication interface 92 could be reduced but is wasted on waiting.
Regarding the host transmission interface 91, according to a master-slave architecture of the host 90 (serving as a master) and the wireless communication apparatus 9 (serving as a slave), a power state of the host transmission interface 91 is controlled by the host 90. That is to say, the host 90 is operable to transmit a command allowing the host transmission interface 91 to enter a low power consuming mode. Under such architecture, control circuits of the host transmission interface 91 must be in the continuous aware mode for fast inspection of signals from the host 90 and for responding to the host 90 within a response time required by the communication protocol so as to maintain normal connection between the host transmission interface 91 and the host 90. Moreover, in order to be ready to receive external packets at any time, the host 90 does not actively reduce power to the host transmission interface 91 in general. Therefore, the host transmission interface 91 does not often enter the low power consuming mode, and the period of entering the low power consuming mode is relatively short such that it is inefficient in saving power. In addition, since power consuming modes of the host transmission interface 91 cooperate with an operating system of the host 90 in general, design on the host transmission interface 91 related to power saving is often neglected.
However, due to development of high speed transmission interfaces, an interface bus with high transmission speed is now used in the host transmission interface 91. As working frequency of control circuits of the interface bus becomes higher, power consumption of the host transmission interface 91 has an increasing proportion in the overall power consumption of the wireless communication apparatus 9. In this situation, power management for the host transmission interface 91 has become relatively important.
Based on available techniques, aside from the above-mentioned disadvantages that the wireless communication interface 92 and the host transmission interface 91 are inefficient in saving power, designs of the wireless communication interface 92 and the host transmission interface 91 for controlling power states thereof are independent from each other. In this situation, for example, when the host transmission interface 91 enters the power saving mode according to the power state set by the host 90, the wireless communication interface 92 may have just been woken up for receiving signals from the communication device 99. Such non-synchronization results in failure to optimize power management for the wireless communication apparatus 9.